The present invention relates to the field of continuous casting of metals, particularly steel, including but not limited to steel alloys, and, more specifically, concerns a new and improved method and apparatus for horizontal continuous casting.
Horizontal continuous casting techniques are enjoying increasing interest in the continuous casting art. Normally the horizontal mold is oscillated in order to obtain a disturbance-free withdrawal of the strand and to realize a satisfactory surface quality of the casting. Between the oscillating mold and the forwardly arranged, stationary tundish from which the molten metal is laterally introduced into the horizontal mold, it is therefore necessary to provide an intermediate space which allows such mold oscillation. However, this transition region between the tundish and the mold is difficult to seal and also poses metallurgical problems.
One possibility of overcoming the need to provide an intermediate space between the tundish and the mold would be to physically connect the tundish with the mold. Still a relatively complex seal would have to be provided at the region where the tundish is connected with the mold. Even so, large masses would have to be placed into oscillating motion, and accordingly, complex and energy-consuming drives would have to be provided for conjointly oscillatingly moving the tundish and mold.
Therefore, in U.S. Pat. No. 4,146,078, granted Mar. 27, 1979 a continuous horizontal casting machine has been disclosed which no longer requires the tundish and mold to be conjointly oscillated. Here, the mold is not attached to the tundish. The liquid metal stream flows horizontally from the stationary tundish into the continuous casting mold through a coil which produces a magnetic field for constricting and confining the molten metal along a defined path of travel as it moves in transit between the exit end of the tundish and the inlet end of the continuous casting mold. With this design, on the one hand, there is safeguarded against any deleterious solidification of the molten metal at the outlet or exit opening of the tundish, and, on the other hand, there is compensated the metallostatic pressure at the intermediate gap between the tundish and the mold. That construction of continuous casting installation only casts a single strand.
The use of an electrical conductor powered by a source of alternating-current for repelling molten metal from an opening, such as the inlet opening of a vertical continuous casting mold, in conjunction with a syphon, is known from U.S. Pat. No. 4,020,890, granted May 3, 1977. However, horizontal continuous casting techniques using a double-ended oscillating horizontal mold are neither taught nor contemplated and the provision of the syphon, specifically the plate-like discharge portion which reposes in or near the level of the molten metal within the vertical casting mold itself contributes to the escape of metal from the mold.
Another prior art method and apparatus for continuously casting metals has been disclosed in U.S. Pat. No. 3,472,309, granted Oct. 14, 1969. There is taught the use of a double-ended oscillating mold of inverted T-shaped configuration which is designed to provide at the vertically extending portion of the mold a reservoir equipped with electrical coils for heating the molten metal infed to such upstanding reservoir by a nozzle in order to make-up the heat losses. The lower end of the vertically extending heated reservoir communicates with two copper chill molds from which there are withdrawn two partially solidified strands in opposite direction. This construction of continuous casting machine requires a complicated T-shaped vertical mold formed of different materials and constituting a considerable mass which must be oscillated. Also, special heating facilities must be provided at the refractory reservoir to keep the molten metal in a heated condition until it can reach the two chill molds where the metal is actually cast into two oppositely withdrawn strands. Moreover, with this prior art construction there arise other drawbacks, especially in terms of the extremely difficult accessibility into the mold and impaired visual inspection possibility for the interior of the mold, as well as the increased metallostatic pressure due to the considerable column of molten metal which is present in the vertical reservoir portion of the mold and so forth. Additionally, such mold construction composed of two metallic horizontal mold portions or chill molds and a vertical reservoir portion composed of refractory material is extremely prone to disturbance and complicated in design. To counteract the danger of freezing of the metal there must be installed in the upstanding vertical refractory portion or reservoir the heating coils.
Also, in U.S. Pat. No. 3,575,230, granted Apr. 20, 1971 there is disclosed a similar inverted T-shaped double-ended continuous casting mold having an upstanding heated reservoir, wherein the same shortcomings are essentially present as discussed above with respect to U.S. Pat. No. 3,472,309.
While in Russian Pat. No. 407,630, dated Apr. 19, 1974 there is disclosed a double-ended horizontal continuous casting mold which does not use such a complicated mold design, and specifically only employs an essentially horizontally extending mold, such construction, however, is not an oscillating mold. The molten metal is introduced from above by a pouring nozzle into the non-oscillating horizontal mold and the two formed strands are withdrawn at opposed ends of the mold in opposite directions. To improve the efficiency and the quality of the formed cast strands it is contemplated to horizontally move the pouring nozzle for the influxing metal jet in the direction of the greater rate of strand withdrawal and at a rate equal to the difference in the rates of withdrawal of the metal strands from opposite ends of the continuous casting mold. The two formed strands are interconnected by a strand shell or skin which, upon withdrawal of the two strands from the continuous casting mold, will be unpredictably severed at a random location. Additionally, it is difficult to exactly control the movement of the nozzle infeeding the metal jet so that at all times uniform conditions prevail within the continuous casting mold. Therefore, it is not possible to produce any uniformly cast strands, particularly since the formation of the strand shell along the circumference of the interconnected two strands is disturbed because of the irregular solidification of the cast strands. Hence, reliable casting of strands with this equipment does not appear to be possible.
In Russian Pat. No. 578,155, dated Jan. 13, 1978 there is disclosed a double-ended non-oscillating continuous casting mold which is formed of both a straight mold portion and a curved mold portion. A pouring nozzle infeeds the molten metal from above into the curved portion of the continuous casting mold, and at the opposed ends of the continuous casting mold the two strands are withdrawn. Through the provision of this relatively complicated mold construction, composed of the differently configured mold portions, it is intended to fix at a predetermined place the rupture or fracture location between both of the oppositely withdrawn strands which move along strand axes inclined with respect to the horizontal. This rupture location is intended to be located at the transition region between the straight and curved mold portions, since at that place there is supposed to be located the weakest, hottest and thinnest portion of the continuously cast strands. If this location were situated in the linear mold portion then such part of the strand could not enter into the curved mold portion. The same undesirable phenomenon would arise if the mentioned location were located in the curved portion of the continuous casting mold. Such type of semi-radial continuous casting installation does not allow for the system to operate reliably since a continuous rupture of the strands occurs. Moreover, uniform solidification conditions for the strands cannot be realized with such casting machine. Since this construction of double-ended mold cannot be oscillated for the reasons explained, there is also not possible any withdrawal of the strands out of the continuous casting mold without danger of damaging the same.